feat: attack chain DAG visualization, report export, and UI polish

- Add interactive attack chain DAG using vis-network with hierarchical
  layout, status-colored nodes, risk-based sizing, and click handlers
- Add pentest session export API (GET /sessions/:id/export) supporting
  both JSON and Markdown report formats
- Redesign attack chain tab with graph/list toggle views
- Add export buttons (MD/JSON) to session header with Blob download
- Show exploitable badge and endpoint on finding cards
- Add export_pentest_report server function for dashboard

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-dashboard/src/infrastructure/pentest.rs

@@ -188,3 +188,24 @@ pub async fn fetch_pentest_findings(
         .map_err(|e| ServerFnError::new(e.to_string()))?;
     Ok(body)
 }
+
+#[server]
+pub async fn export_pentest_report(
+    session_id: String,
+    format: String,
+) -> Result<String, ServerFnError> {
+    let state: super::server_state::ServerState =
+        dioxus_fullstack::FullstackContext::extract().await?;
+    let url = format!(
+        "{}/api/v1/pentest/sessions/{session_id}/export?format={format}",
+        state.agent_api_url
+    );
+    let resp = reqwest::get(&url)
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))?;
+    let body = resp
+        .text()
+        .await
+        .map_err(|e| ServerFnError::new(e.to_string()))?;
+    Ok(body)
+}